The study from the University of Pennsylvania and the Naval Health Research Center found that pre-existing insomnia symptoms were almost as big of a risk for those mental disorders as exposure to combat. Using self-reported data from the Millennium Cohort Study, collected from members of the military who had been deployed to Iraq or Afghanistan, the research team evaluated the association of pre-deployment sleep duration and insomnia on the development of new mental disorders after deployment.

They analysed data from 15,204 service members after their first deployment. They identified 522 people with new-onset PTSD, 151 with anxiety, and 303 with depression following deployment. The researchers found that combat-related trauma and pre-deployment insomnia symptoms were “significantly associated” with higher odds of developing PTSD, depression, and anxiety. “One of the more interesting findings of this study is not only the degree of risk conferred by pre-deployment insomnia symptoms, but also the relative magnitude of this risk compared with combat-related trauma,” said lead study author Philip Gehrman, Ph.D., an assistant professor of psychology. “The risk conferred by insomnia symptoms was almost as strong as our measure of combat exposure in adjusted models.”

The researchers also found that short sleep duration — described as less than six hours of sleep a night — also was associated with new-onset PTSD symptoms. “We found that insomnia is both a symptom and a risk factor for mental illness and may present a modifiable target for intervention among military personnel,” Gehrman said. “We hope that by early identification of those most vulnerable, the potential exists for the designing and testing of preventive strategies that may reduce the occurrence of PTSD, anxiety and depression.”